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Subject: Re: [PATCH v15 7/9] nvmet-passthru: Add passthru code to process
 commands
To:     Keith Busch <kbusch@kernel.org>
Cc:     Logan Gunthorpe <logang@deltatee.com>,
        Chaitanya Kulkarni <Chaitanya.Kulkarni@wdc.com>,
        linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
        Stephen Bates <sbates@raithlin.com>, Jens Axboe <axboe@fb.com>,
        Max Gurtovoy <maxg@mellanox.com>,
        Christoph Hellwig <hch@lst.de>
References: <20200716203319.16022-1-logang@deltatee.com>
 <20200716203319.16022-8-logang@deltatee.com> <20200720141606.GF4627@lst.de>
 <e939dd43-9e7f-8ef0-162b-2a27f53e6e1a@grimberg.me>
 <5cc390cf-9b0b-b48b-7447-37934be51ee0@deltatee.com>
 <2dc39232-4042-1f93-3dcc-3266e70cf6f0@grimberg.me>
 <b8fc47a2-0b53-3316-775f-0e9a8eddfdc2@deltatee.com>
 <20200720231701.GA682160@dhcp-10-100-145-180.wdl.wdc.com>
 <d7596065-f33b-5533-7254-153b82e6b88b@grimberg.me>
 <20200721000630.GA682317@dhcp-10-100-145-180.wdl.wdc.com>
From:   Sagi Grimberg <sagi@grimberg.me>
Message-ID: <be06756a-bb05-ae83-3aea-6eb97d985160@grimberg.me>
Date:   Mon, 20 Jul 2020 17:39:04 -0700
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>>> On Mon, Jul 20, 2020 at 05:01:19PM -0600, Logan Gunthorpe wrote:
>>>> On 2020-07-20 4:35 p.m., Sagi Grimberg wrote:
>>>>
>>>>> passthru commands are in essence REQ_OP_DRV_IN/REQ_OP_DRV_OUT, which
>>>>> means that the driver shouldn't need the ns at all. So if you have a
>>>>> dedicated request queue (mapped to the I/O tagset), you don't need the
>>>>> ns->queue and we can lose the ns lookup altogether.
>>>
>>> We still need a request_queue to dispatch the command. I guess you could
>>> make a generic one for the controller that isn't tied to a namespace,
>>> but we lose the fair shared tag allocation.
>>
>> What do you mean fair shared tag allocation?
> 
> See hctx_may_queue().

Still not following your point... this queue is yet another request
queue on the I/O tagset, e.g.

ctrl->passthru_q = blk_mq_init_queue(ctrl->tagset);